Binder for pressure sensitive adhesive

Abstract

Binder for a pressure sensitive adhesive, characterized in that it exists as a polymer dispersed in water and obtained by emulsion polymerization of: (A) 65.0-99.4 percent by weight of one or more acrylic esters with 4-18, preferably 6-10 carbon atoms in the alcohol part of the ester, the esters being selected in such a way that a polymerization of only these esters gives a tacky polymer with a Tg-value below 0 DEG C., preferably below -20 DEG C. (B) 2.0-0.1 percent by weight of a polymerizable compound with the formula <IMAGE> or with the formula <IMAGE> wherein R1, R2, R3 and R4 are as defined in the specification (C) 5.0-0.5 percent by weight of at least one ethylenically unsaturated acid such as acrylic acid, methacrylic acid or itaconic acid and (D) 28.0-0 percent by weight of one or more compounds selected from the group consisting of alkyl- or hydroxyalkyl acrylate or a lower alkyl or hydroxyalkyl methacrylate with 1-3 carbon atoms in the alcohol part of the ester, acrylonitrile or styrene.

We claim: 
     
       1. Process for the production of a binder for a pressure sensitive adhesive by emulsion polymerization of: (A) 65-99.4 percent by weight of at least one acrylic ester with 4-18 carbon atoms in the alcohol part of the ester, the esters being selected whereby polymerization of only the selected esters produces a tacky polymer with a Tg-value below 0° C.;   (B) 0.1 to 2 percent by weight of a polymerizable compound selected from the group consisting of a compound of the formula ##STR6##  where R 1  =H or CH 3 , R 2  =H or ##STR7## and R 3  =CH 3 , C 2  H 5 , OH, CH 2  OH or ##STR8## or a compound with the formula ##STR9##  where R 4  =CH 3  or CH 2  CH=CH 2  (C) 5-0.5 percent by weight of at least one ethylenically unsaturated acid and     (D) 28-0 percent by weight of one or more compounds selected from the group consisting of an alkyl acrylate, a hydroxyalkyl acrylate, a lower alkyl methacrylate, a hydroxyalkyl methacrylate with 1-3 carbon atoms in the alcohol part of the ester, acrylonitrile or styrene, said process comprising first copolymerizing the compounds from the groups (A), (C) and (D) in water at a temperature of about 40°-90° C. for 1/4 to 7/8 of the total reaction time, and then mixing therewith a compound from group (B) and completing the reaction.   
     
     
       2. The process of claim 1 wherein the compounds from the groups (A), (C) and (D) are first copolymerized for 1/2 to 4/5 of the total reaction time, the compounds from group (B) are mixed therewith, and the reaction is completed. 
     
     
       3. The process of claim 1 or 2 wherein the total reaction time is about 4 hours. 
     
     
       4. The process of claim 1 or 2 wherein 78-98.9 percent by weight of one or more compounds from group (A), 1-0.1 percent by weight of one or more compounds from group (B), 3-1 percent by weight of at least one compound from group (C) and 18-0 percent by weight of one or more compounds from group (D) are copolymerized. 
     
     
       5. The process of claim 1 or 2 wherein A is ethylhexyl acrylate, butyl acrylate, ethyl acrylate or a mixture thereof, B is trimethylol propane triacrylate, trimethylol propane trimethacrylate, pentaerythritol triacrylate, tetraallyloxy ethane or a mixture thereof,   C is at least one of the compounds acrylic acid or methacrylic acid, and   D is acrylonitrile, methyl acrylate, methyl methacrylate or styrene.